This application claims the benefit of a Japanese Patent Application No.2001-111913 filed Apr. 10, 2001, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to DC-DC converters and storage apparatuses, and more particularly to a DC-DC converter which is suited for reducing power consumption of an apparatus, and to a storage apparatus which is provided with such a DC-DC converter.
A disk unit, such as a magnetic disk unit, can be used as a storage apparatus of a host unit such as a personal computer. Recently, there are increased demands to increase the processing speed and to reduce the power consumption of the disk unit. The reduction of the power consumption of the disk unit is important particularly when the disk unit is used as the storage apparatus of a portable personal computer which is driven by a battery.
2. Description of the Related Art
Among various kinds of large scale integrated (LSI) circuits provided within the disk unit, some LSI circuits use mutually different external power supply voltages in order to bring out respective performances to a maximum. For example, there are LSI circuits which use power supply voltages of 2.6 V, 2.5 V, 1.8 V, 1.5 V or the like.
FIG. 1 is a circuit diagram showing an example of a conventional DC-DC converter. The DC-DC converter includes an operational amplifier 1, a transistor Q, and a capacitor Cf which are connected as shown in FIG. 1. Vcc denotes an external power supply voltage, Vref denotes a reference voltage, Vout denotes an internal power supply voltage after conversion supplied to an LSI circuit or the like, and GND denotes the ground.
A power P consumed by the transistor Q can be described by P=(Vccxe2x88x92Vref)xc3x97Iout, where Iout denotes an output current, and this power becomes the loss. By reducing the external power supply voltage Vcc supplied to the LSI circuit via the DC-DC converter, it is possible to suppress an increase of the power consumption of the LSI circuit itself, but the current consumption of the LSI circuit increases. For example, in a case where the external power supply voltage Vcc with respect to the LSI circuit having a power consumption Pd of Pd=1 W is Vcc=2.5 V, a current consumption Ic of the LSI circuit via the DC-DC converter becomes Ic=0.4 A from a relationship Pd=Vccxc3x97Ic. On the other hand, in a case where the external power supply voltage Vcc with respect to the LSI circuit is Vcc=5 V, the current consumption Ic of the LSI circuit via the DC-DC converter becomes Ic=0.2 A. Hence, it may be seen that the current consumption Ic of the LSI circuit increases by 0.2 A when the external power supply voltage Vcc decreases by 2.5 V.
Therefore, in the conventional DC-DC converter, the increase of the power consumption of the LSI circuit itself can be suppressed by reducing the external power supply voltage, but the current consumption of the LSI circuit increases. In other words, the conventional DC-DC converter is a series regulator, and there was a problem in that the power consumption of the disk unit as a whole increases as a result.
In order to reduce the power consumption of the disk unit, it is conceivable to supply the external power supply voltage to the LSI circuit via a switching regulator. However, a large spike noise is generated in the internal power supply voltage when the switching regulator is used, to thereby deteriorate the performance of the disk unit. In addition, when a filter or the like is provided to reduce the spike noise, the structure of the disk unit as a whole becomes complex, and the cost of the disk unit is also increased thereby.
Accordingly, it is a general object of the present invention to provide a novel and useful DC-DC converter and storage apparatus, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a DC-DC converter and a storage apparatus, which can supply a low power supply voltage with a high efficiency.
Still another object of the present invention is to provide a DC-DC converter comprising N capacitors having identical capacitances, initially coupled in series, and supplied with an external power supply voltage to be charged thereby, and means for coupling the N capacitors in parallel and varying a duty ratio of a charging timing, so as to vary an internal power supply voltage which is output from the DC-DC converter. According to the DC-DC converter of the present invention, it is possible to supply a low power supply voltage with a high efficiency.
A further object of the present invention is to provide a DC-DC converter comprising N first capacitors having identical capacitances, initially coupled in series, and M second capacitors, initially coupled in parallel to each other and in parallel to the N first capacitors, respectively supplied with an external power supply voltage to be charged thereby, and means for coupling the N first capacitors in parallel to each other, and the M second capacitors in series to each other and in series to the N first capacitors, and varying a duty ratio of a charging timing, so as to vary an internal power supply voltage which is output from the DC-DC converter. According to the DC-DC converter of the present invention, it is possible to supply a low power supply voltage with a high efficiency.
Another object of the present invention is to provide a DC-DC converter comprising switching means for coupling N capacitors having identical capacitances in series in a first connection state and supplying thereto an external power supply voltage to be charged thereby, and for coupling the N capacitors in parallel in a second connection state, and varying means for varying a duty ratio of a charging timing of the N capacitors in the first connection state, so as to output an internal power supply voltage which is variable. According to the DC-DC converter of the present invention, it is possible to supply a low power supply voltage with a high efficiency.
Still another object of the present invention is to provide a DC-DC converter comprising switching means for coupling N first capacitors having identical capacitances in series, and coupling M second capacitors in parallel to each other and in parallel to the N first capacitors in a first connection state, and supplying thereto an external power supply voltage to be charged thereby, and for coupling the N first capacitors in parallel to each other and the M second capacitors in series to each other and in series to the N first capacitors in a second connection state, and varying means for varying a duty ratio of a charging timing of the N first capacitors and the M second capacitors in the first connection state, so as to output an internal power supply voltage which is variable. According to the DC-DC converter of the present invention, it is possible to supply a low power supply voltage with a high efficiency.
A further object of the present invention is to provide a DC-DC converter comprising a switching circuit which couples N capacitors having identical capacitances in series in a first connection state and supplies thereto an external power supply voltage to be charged thereby, and couples the N capacitors in parallel in a second connection state, and a circuit which varies a duty ratio of a charging timing of the N capacitors in the first connection state, so as to output an internal power supply voltage which is variable. According to the DC-DC converter of the present invention, it is possible to supply a low power supply voltage with a high efficiency.
Another object of the present invention is to provide a DC-DC converter comprising a switching circuit which couples N first capacitors having identical capacitances in series, and couples M second capacitors in parallel to each other and in parallel to the N first capacitors in a first connection state, and supplies thereto an external power supply voltage to be charged thereby, and couples the N first capacitors in parallel to each other and the M second capacitors in series to each other and in series to the N first capacitors in a second connection state, and a circuit which varies a duty ratio of a charging timing of the N first capacitors and the M second capacitors in the first connection state, so as to output an internal power supply voltage which is variable. According to the DC-DC converter of the present invention, it is possible to supply a low power supply voltage with a high efficiency.
Still another object of the present invention is to provide a storage apparatus comprising an internal circuit, a storage section, and a DC-DC converter which supplies an internal power supply voltage to the internal circuit, where the DC-DC converter comprises switching means for coupling N capacitors having identical capacitances in series in a first connection state and supplying thereto an external power supply voltage to be charged thereby, and for coupling the N capacitors in parallel in a second connection state, and varying means for varying a duty ratio of a charging timing of the N capacitors in the first connection state, so as to output an internal power supply voltage which is variable. According to the storage apparatus of the present invention, it is possible to supply a low power supply voltage with a high efficiency.
A further object of the present invention is to provide a storage apparatus comprising an internal circuit, a storage section, and a DC-DC converter which supplies an internal power supply voltage to the internal circuit, where the DC-DC converter comprises switching means for coupling N first capacitors having identical capacitances in series, and coupling M second capacitors in parallel to each other and in parallel to the N first capacitors in a first connection state, and supplying thereto an external power supply voltage to be charged thereby, and for coupling the N first capacitors in parallel to each other and the M second capacitors in series to each other and in series to the N first capacitors in a second connection state, and varying means for varying a duty ratio of a charging timing of the N first capacitors and the M second capacitors in the first connection state, so as to output an internal power supply voltage which is variable. According to the storage apparatus of the present invention, it is possible to supply a low power supply voltage with a high efficiency.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.